SKULL— SAUROPSIDA 135 



Among the characteristics of the Amniote chondrocranium, so far 

 as known, are its tropibasic structure (fig. 144), the paired trabeculae 

 uniting to a trabecula communis just in front of the hypophysis, 

 leaving a small hypophysial fenestra. To accommodate the greatly 

 enlarged lagena of the ear, this organ has invaded at least the basal 

 plate. The nasal capsule is more comphcated, one feature being 

 the paraseptal cartilages, primarily connected with the floor of the 

 capsule and protecting the vomero-nasal organ. The pterygoid arch 

 is reduced, never reaching the nasal capsule. The roof of the 

 cranium is reduced to the synotic tectum and the occipital region. 

 The branchial arches, in correlation with the loss of branchial respira- 

 tion, are reduced and modified for other functions, and some arches 

 are entirely lost. 



In the adult skull may be noted the ossification of basi- and 

 supraoccipital, and also a basisphenoid, unknown in Amphibia, 

 while the parasphenoid, so large in Amphibia, is greatly reduced or 

 even lost. When present it is usually fused with the basisphenoid 

 or presphenoid, when apparently lost, some maintain (p. 77) it to 

 be represented by the vomer. Another feature is the suspensor of 

 the lower jaw, which, as shown by Teleostomes, was originally 

 movable on the cranium (streptostylic). This condition exists in 

 Squamata and birds (probably secondary) and in mammals where 

 the homologue of the quadrate (incus) is free, although its suspen- 

 sorial function has gone. All other reptiles (Monimostyhca) have 

 an immovable quadrate, it being fixed by the squamosal and 

 frequently by other bones. 



There is also a reduction and fusion of some of the visceral arches, 

 some contributing to the hyoid apparatus, in which three arches at 

 most are concerned, while there is a probabiliy that the hyoid has 

 contributed to the ossicula auditus (p. 119). The more posterior 

 arches may take part in the laryngeal and bronchial cartilages. The 

 hyoid apparatus is ventral to the larynx, and in many groups, in 

 contrast to the Ichthyopsida, it supports a true tongue. 



SAUROPSIDA. — Among features common to the skulls of both 

 reptiles and birds are: i, the lack of a chondrocranial roof aside from 

 the synotic tectum; an entire independence of the pterygoquadrate 

 cartilage, and often a separation of quadrate and pterygoid parts, 

 the whole bar being weakly developed; 2, a single occipital condyle 

 largely or wholly on the basioccipital, although in the embryo and 



