CROCODILIA. 21 



T. I. In the Gavials (T. XI, fig. 1 a) the nasals (n) terminate a long way from the 

 nostril. The Crocodilia resemble the Chelonia in the single median nostril.* In the 

 Lacertilia there is a pair of nostrils, one on each side the median plane, which is 

 occupied by a bridge of bone extending from the usually single premaxillary to the 

 nasals. The plane of the single nostril is almost horizontal in all existing and tertiary 

 Crocodilia. 



On the inferior or palatal surface of the skull (T. VII, fig. 2), the most anterior 

 aperture is the circular prepalatal foramen surrounded by the premaxillaries 22 ; then 

 follows an extensive smooth, horizontal, bony plate, formed by the premaxillaries (22), 

 the maxillaries (21), and the palatines (20) . The postpalatal apertures are always large 

 in the Crocodilia, and are bounded by the palatines (20), maxillaries (21), pterygoids (24), 

 and ectopterygoids (25). The posterior aperture of the nostril is formed wholly by the 

 pterygoids ; it is shown in T. VI, fig. 3, between the bones marked 24. Behind it is 

 the median and lateral eustachian foramen already described, as belonging rather to 

 the posterior region of the head. 



The scapido-coracoid arch, both elements (fig. 9, 51, 52) of which retain the form of 

 strong and thick vertebral and sternal ribs in the crocodile, is applied in the skeleton of 

 that animal over the anterior thoracic haemal arches (T. XI), Viewed as a more robust 

 haemal arch, it is obviously out of place in reference to the rest of its vertebral segment. 

 If we seek to determine that segment by the mode in which we restore to their centrums 

 the less displaced neural arches of the antecedent vertebrae of the cranium or in the 

 sacrum of the bird,f we proceed to examine the vertebrae before and behind the dis- 

 placed arch, with the view to discover the one which needs it, in order to be made 

 typically complete. Finding no centrum and neural arch without its pleurapophyses 

 from the scapula to the pelvis, we give up our search in that direction ; and in the 

 opposite direction we find no vertebra without its ribs until we reach the occiput : 

 there we have centrum and neural arch, with coalesced parapophyses — the elements 

 answering to those included in the arch Ni, fig. 9 — but without the arch H i; which 

 arch can only be supplied, without destroying the typical completeness of antecedent 

 cranial segments, by a restoration of the bones 50 — 52, to the place which they 

 naturally occupy in the skeleton of the fish. And since anatomists are generally 

 agreed to regard the bones 50 — 52 in the crocodile as specially homologous with 

 those so numbered in the fish,;}: we must conclude that they are likewise homologous 

 in a higher sense ; that in the fish, the scapulo-coracoid arch is in its natural or 

 typical position, whereas in the crocodile it has been displaced for a special purpose. 

 Thus, agreeably with a general principle, we perceive that, as the lower vertebrate 



* In a skeleton of the Alligator lucius in the Museum of the Royal College of Surgeons, a slender bar 

 of bone is continued from the nasals to the premaxillary, across the median nasal aperture, as it is in the 

 skull of the same species figured in the 'Ossemens Fossiles,' torn, v, pt. ii, pi. i, fig. 8. 



f See 'On the Archetype and Homologies of the Vertebrate Skeleton,' p. 117, p. 159. 



% Op. cit., fig. 5, p. 17. 



