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Numerous human syndromes are characterized by congenital heart defects and craniofacial anomalies. This is because the development of the head and heart are closely related. Several studies revealed that specific regions of the myocardium are closer related to specific head muscle groups than to other myocardial regions. The gene regulatory network underlying the specification and differentiation of cardiac and branchiomeric musculature from a common progenitor field, the cardiopharyngeal field, is just starting to get revealed. However, every single new insight into the evolution and development of the head and heart tissues contributes to our understanding of complex human syndromes. Here, I summarize the most recent finding regarding the underlying mechanisms for the proper head and heart musculature development and indicate syndromes, e.g., DiGeorge syndrome and Axenfeld-Rieger syndrome, that might be better understood due to those new insights.

Animal body parts evolve with variable degrees of integration that nonetheless yield functional adult phenotypes: but, how? The analysis of modularity with Anatomical Network Analysis (AnNA) is used to quantitatively determine phenotypic modules based on the physical connection among anatomical elements, an approach that is valuable to understand developmental and evolutionary constraints. We created anatomical network models of the head, forelimb, and hindlimb of two taxa considered to represent a ‘generalized’ eutherian (placental: mouse) and metatherian (marsupial: opossum) anatomical configuration and compared them with our species, which has a derived eutherian configuration. In these models, nodes represent anatomical units and links represent their physical connection. Here, we aimed to identify: (1) the commonalities and differences in modularity between species, (2) whether modules present a potential phylogenetic character, and (3) whether modules preferentially reflect either developmental or functional aspects of anatomy, or a mix of both. We predicted differences between networks of metatherian and eutherian mammals that would best be explained by functional constraints, versus by constraints of development and/or phylogeny. The topology of contacts between bones, muscles, and bones + muscles showed that, among all three species, skeletal networks were more similar than musculoskeletal networks. There was no clear indication that humans and mice are more alike when compared to the opossum overall, even though their musculoskeletal and skeletal networks of fore- and hindlimbs are slightly more similar. Differences were greatest among musculoskeletal networks of heads and next of forelimbs, which showed more variation than hindlimbs, supporting previous anatomical studies indicating that in general the configuration of the hindlimbs changes less across evolutionary history. Most observations regarding the anatomical networks seem to be best explained by function, but an exception is the adult opossum ear ossicles. These ear bones might form an independent module because the incus and malleus are involved in forming a functional primary jaw that enables the neonate to attach to the teat, where this newborn will complete its development. Additionally, the human data show a specialized digit 1 module (thumb/big toe) in both limb types, likely the result of functional and evolutionary pressures, as our ape ancestors had highly movable big toes and thumbs., BE-A has received financial support through the Postdoctoral Junior Leader Fellowship Program from “la Caixa” Banking Foundation (LCF/BQ/LI18/11630002) and thanks to the support of the Unidad de Excelencia María de Maeztu (MDM-2014-0370). JCB is supported by the Canada Foundation for Innovation (CFI; JCB #29037), the Natural Sciences and Engineering Research Council of Canada (NSERC; JCB #2016-05177), and a College of Medicine Research Award.

The triceps brachii muscle occupies the posterior compartment of the arm in humans and has three heads. The lateral and medial heads originate from the humerus and the long head arises from the infraglenoid tubercle of the scapula. All heads form a common tendon that inserts onto the olecranon and the deep antebrachial fascia on each side of it. Each head receives its own motor branch, which all are thought to originate from the radial nerve. However, several studies reported that the motor branch of the long head of the triceps (LHT) arises from the axillary nerve or the posterior cord. Here, we dissected 27 triceps in 15 cadavers to analyze the innervation of the LHT and found only radial innervation, which contradicts those studies. We examined studies reporting that the motor branch to the LHT in humans does not arise from the radial nerve as well as studies of the triceps in primates. Occasional variations of the innervation of skeletal muscles are normal, but a change of principal motor innervation from radial to axillary nerve has important implications. This is because the axillary nerve is often involved during shoulder injuries. The precise identification of the prevalence of axillary versus radial innervation is therefore clinically relevant for surgery, nerve drafting, and occupational and physical therapy. We conclude that the primary motor branch to the LHT arises from the radial nerve but axillary/posterior cord innervations occur occasionally. We suggest the development of a standard methodology for further studies. Anat Rec, 301:473-483, 2018. © 2018 Wiley Periodicals, Inc.

Few descriptions of the musculoskeletal system of humans with anencephaly or spina bifida exist in the literature. Even less is published about individuals in which both phenomena occur together, i.e. about craniorachischisis. Here we provide a detailed report on the musculoskeletal structures of a fetus with craniorachischisis, as well as comparisons with the few descriptions for anencephaly and with musculoskeletal anomalies found in other congenital malformations. We focused in particular on the comparison with trisomies 13, 18, and 21 because neural tube defects have been associated with such chromosomal defects. Our results showed that many of the defects found in the fetus with craniorachischisis are similar not only to anomalies previously described in the available works on musculoskeletal phenotypes seen in fetuses with anencephaly and spina bifida, but also to a wide range of other different conditions/syndromes including trisomies 13, 18 and 21, and cyclopia. The fact that similar anomalies are seen commonly not only in a wide range of different syndromes, but also as variants of the normal human population and as the 'normal' phenotype of other animals, supports Pere Alberch's unfortunately named idea of a 'logic of monsters'. That is, it supports the idea that development is so constrained that both in 'normal' and abnormal development one sees certain outcomes being produced again and again because ontogenetic constraints only allow a few possible outcomes, thus also leading to cases where the anatomical defects of some organisms are similar to the 'normal' phenotype of other organisms. In fact, this applies not only to specific anomalies but also to general patterns, such as the fact that in pathological conditions affecting different regions of the body, one consistently sees more defects on the upper limbs than on the lower limbs. Such general patterns are, again, seen in the fetus examined for this study, which had 29 muscle anomalies on the right upper limb and 22 muscle anomalies on the left upper limb, vs. seven muscle anomalies on the right lower limb and two on the left lower limb. It is therefore hoped that this work, which is part of our effort to describe and compile information on human musculoskeletal defects found in a wide range of conditions, will contribute not only to a better understanding of craniorachischisis in particular and of human congenital malformations in general, but also to broader discussions on the fields of comparative anatomy, and developmental and evolutionary biology.

It is usually assumed that Galen is one of the fathers of anatomy and that between the Corpus Galenicum and the Renaissance there was no major advance in anatomical knowledge. However, it is also consensually accepted that Muslim scholars had the intellectual leadership from the 8th/9th to 13th centuries, and that they made remarkable progresses in numerous scientific fields including medicine. So, how is it possible that they did not contribute to advance human anatomy during that period? According to the dominant view, Muslim scholars exclusively had a passive role: their transmission of knowledge from the Greeks to the West. Here, we summarize, for the first time in a single paper, the studies of major Muslim scholars that published on human anatomy before Vesalius. This summary is based on analyses of original Arabic texts and of more recent publications by anatomists and historians, and on comparisons between the descriptions provided by Galen and by these Muslim scholars. We show that Arabic speakers and Persians made important advances in human anatomy well before Vesalius. The most notable exception concerns the muscular system: strikingly, there were apparently neither advances made by Muslims nor by Westerners for more than 1000 years. Unbiased discussions of these and other related issues, and particularly of the mainly untold story about the major contributions of Muslim scholars to anatomy, are crucial to our knowledge of the history of anatomy, biology and sciences, and also of our way of thinking, biases, and prejudices. Anat Rec, 300:986-1008, 2017. © 2017 Wiley Periodicals, Inc.

Textbooks on the history of biology and evolutionary thought do not mention the evolutionary ideas of Muslim scholars before Darwin’s time. This is part of a trend in the West to minimise the contr...

The ill-named “logic of monsters” hypothesis of Pere Alberch - one of the founders of modern evo-devo - emphasized the importance of “internal rules” due to strong developmental constraints, linked teratologies to developmental processes and patterns, and contradicted hypotheses arguing that birth defects are related to a chaotic and random disarray of developmental mechanisms. We test these hypotheses using, for the first time, anatomical network analysis (AnNA) to study and compare the musculoskeletal modularity and integration of both the heads and the fore- and hindlimbs of abnormal cyclopic trisomy 18 and anencephalic human fetuses, and of normal fetal, newborn, and adult humans. Our previous works have shown that superficial gross anatomical analyses of these specimens strongly support the “logic of monsters” hypothesis, in the sense that there is an ‘order’ or ‘logic’ within the gross anatomical patterns observed in both the normal and abnormal individuals. Interestingly, the results of the AnNA done in the present work reveal a somewhat different pattern: at least concerning the musculoskeletal modules obtained in our AnNA, we observe a hybrid between the “logic of monsters” and the “lack of homeostasis” hypotheses. For instance, as predicted by the latter hypothesis, we found a high level of left-right asymmetry in the forelimbs and/or hindlimbs of the abnormal cyclopic trisomy 18 and anencephalic human fetuses. That is, a network analysis of the organization of/connection between the musculoskeletal structures of these fetuses reveals a more “chaotic” pattern than that detected by superficial gross anatomical comparisons. We discuss the broader developmental, evolutionary, and medical implications of these results.

Extant cyclostomes are jawless vertebrates and include hagfishes and lampreys. They are the closest extant relatives to jawed vertebrates (often called gnathostomes, which also include jawless extinct species) and share with them vertebrate-specific characters, like the presence of somites, neural crest cells, eyes (absent in hagfish), among others. There are also cyclostome-specific characteristics as the lingual apparatus, velum, and posterior hypophyseal process-derived cartilages. The comparison of development and anatomy between cyclostomes and gnathostomes provides insights into the evolution of the jaws and associated muscles. Furthermore, comparative anatomical and evolutionary developmental studies help to reconstruct the last common ancestor of vertebrates, cyclostomes, and gnathostomes. The evolutionary appearance of the jaw and associated muscles is of particular interest, as those are said to be one of the main reasons for the success of jawed vertebrates. Interestingly, the mechanisms to make an upper jaw are in place in cyclostomes and jawed vertebrates, but the lower jaw developmental program is only found in gnathostomes. The lower jaw is therefore a novelty that evolved in gnathostomes. Another example is the mandibular arch mesoderm and the associated neural crest cells which give rise to mandibular arch muscles and the jaws in gnathostomes, respectively. Cyclostomes have many muscles derived from the mandibular arch mesoderm, but only few can be homologized with those muscles from gnathostomes. However, those muscles that are homologous between those taxa must be present in their last common ancestor, i.e., vertebrates. Interestingly, some studies seem to indicate that mandibular arch (first arch) development was only secondarily included in the vertebrate branchial arch series, what would explain several differences in mandibular arch development between jawed and jawless vertebrates. However, this hypothesis is controversially discussed.

Recent findings that urochordates are the closest sister group of vertebrates have dramatically changed our understanding of chordate evolution and of the origin of the vertebrate head and its muscles. To better understand the evolution and diversity of chordates, in particular the morphological and taxonomical diversity of the vertebrates, it is crucial to investigate the origin, development, and comparative anatomy of not only hard tissues but also of soft tissues such as muscles. Building on the recent discovery of the cardiopharyngeal field in urochordates and on the comparative anatomy of chordate and vertebrate muscles, in this chapter we focus on the broader comparative and developmental anatomy of chordate muscles and the origin of vertebrate cephalic muscles.

Living amphibians include caecilians, salamanders, and frogs. They share many features like a biphasic lifestyle with aquatic larvae and terrestrial adults, cranial skeletal elements that are derived from neural crest cells and mesoderm, and muscles derived from branchiomeric mesoderm and somites. Meckel’s cartilage, which forms the larval lower jaw, derives, for example, from mandibular arch neural crest cells. Mandibular arch mesoderm gives rise to the intermandibularis muscle, which forms the floor of the mouth, and the adductor mandibulae muscles, which are laterally located muscles that close the jaw. For the following arches (hyoid and branchial arches), similarities in muscles and cartilages can also be found. However, taking a closer look, it turns out that amphibians differ also in many things. Direct development evolved in all three taxa as did neoteny, i.e., the specimens reach sexual maturity while still having larval characters. The crania range from robust in caecilians to very light in anurans. Neural crest cells contribute in different amounts to the same cranial structures as the skull roof, and in all muscle groups, some muscles changed their attachments, others are only present in one or two taxa, and again others developed several heads. The knowledge of the diversity and in particular the similarities of amphibian crania and cranial muscles can help us to shed light onto the anatomy of the last common ancestor of tetrapods and onto variations in head anatomy and development in amniotes, which include reptiles and mammals.