. Elements of the comparative anatomy of vertebrates. Anatomy, Comparative. 138 COMPARATIVE ANATOMY undero-oes more or less reduction. Thus various conditions of the ventral musculature are found amongst Qrodeles. In the Anura, on the other hand, both primary and secondary muscles present a marked uniformity and relative simplicity; in the adult they give rise to a segmented rectus, an obliguus externus, and a transversalis, as well as to a cutaneus abdominis derived from the external oblique. No trace of an internal oblique can be seen in the adult. Reptiles.—In Eeptiles, the lateral muscles
. Elements of the comparative anatomy of vertebrates. Anatomy, Comparative. 138 COMPARATIVE ANATOMY undero-oes more or less reduction. Thus various conditions of the ventral musculature are found amongst Qrodeles. In the Anura, on the other hand, both primary and secondary muscles present a marked uniformity and relative simplicity; in the adult they give rise to a segmented rectus, an obliguus externus, and a transversalis, as well as to a cutaneus abdominis derived from the external oblique. No trace of an internal oblique can be seen in the adult. Reptiles.—In Eeptiles, the lateral muscles of the trunk attain a much higher grade of development. This is to be accounted ATe BM. Pig. 116.—The ilusoDLATUBB of SiredonpisciformU. (From the side.) LI, lateral line ; D, dorsal, and F, ventral portion of caudal muscles ; BIC, dorsal portion of lateral muscles of the trunk ; 0, 0, outer layer of the external oblique muscle, arising from the lateral line, and extending to the fascia, F; at * a piece of this layer is removed, exposing the inner layer of the muscle (06); at Be the oblique fibres of the latter pass into longitudinal fibres, indicating the beginning of the differentiation of a rectus abdominis ; at Re^ the rectus-system is seen passing to the visceral skeleton ; Mc, fibrous parti- tions between the myotomes of the dorsal portion of the lateral muscles ; T, temporal; 3£a, masseter ; Dg, digastric ; il/A', mylohyoid (posterior portion); Ce, external ceratohyoid muscle ; Lf, levator arcuum branchialium; +tt, levator branchiarum ; Cph, cervical origin of the constrictor of the pharynx ; Th, thymus; Lt, latissimus dorsi ; Ds, dorsalis scapulee ; Cit, cucullaris; SS, snprascapula ; Ph, procoraoo-humeralis. for by the more perfect condition of the skeleton, more especially of the ribs and pectoral arch. The ribs and intercostal muscles now play an important part in respiration, and changes, necessitated by the more important development of the lungs, are thus bro
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