. Text book of vertebrate zoology. Vertebrates; Anatomy, Comparative. SKELETON. IS7 of a complicated cartilaginous framework, the vertical bars being united by horizontal rods. There occur in connection with the cranium several cartilaginous bars, while in front a series of plates extend to the end of the head. There is no structure comparable beyond a doubt to a hyoid; while instead of mova- bly articulated jaws, the mouth is supported by a cartilaginous ring, and a well-developed cartilaginous framework exists in the tongue, while the filaments around the mouth (^Myxine) have cartilaginous s
. Text book of vertebrate zoology. Vertebrates; Anatomy, Comparative. SKELETON. IS7 of a complicated cartilaginous framework, the vertical bars being united by horizontal rods. There occur in connection with the cranium several cartilaginous bars, while in front a series of plates extend to the end of the head. There is no structure comparable beyond a doubt to a hyoid; while instead of mova- bly articulated jaws, the mouth is supported by a cartilaginous ring, and a well-developed cartilaginous framework exists in the tongue, while the filaments around the mouth (^Myxine) have cartilaginous supports. In the elasmobranchs the skull is never converted into bone, although calcareous deposits may be formed in its wall. The cranium is a closed cap- sule, sometimes carti- laginous throughout, sometimes with places in its roof(fontanelles), which are not chondri- fiied, but are closed with membrane. Through the walls are openings for the passage of nerves and blood-ves- sels, but there is no trace of division into separate elements. The pterygoquadrate in the normal sharks is united to the chondrocranium by liga- ments and muscles, and by the hyomandibular suspensor. In the holocephali, on the other hand, pterygoquadrate and cra- nium are firmly anchylosed in the adult (Fig. i66), although free in the young. Above the elasmobranchs bones appear in the skull, both as ossifications of cartilage and as membrane bones. The more constant and more important of these are as follows : — The chondrocranium gives rise to four bones around the large opening (foramen magnum) through which the brain is connected with the spinal cord. These are, below, the basi- occipital; on either side an exoccipital; and above, part of a. Fig. i66. Skull of Chimara monstrosa (drawn from a dry specimen).. Please note that these images are extracted from scanned page images that may have been digitally enhanced for readability - coloration and appearance of these illustrations may not perfectly rese
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