THE OSTEOLOGY OF AMIURUS CATUS. 283 



valuable suggestions. His paper coming to hand after the previous 

 descriptive portion had been written, explains the homology of the 

 cavity described as occurring in the upper surfaces of the pterotic, 

 supraoccipital, and epiotic. He shows that a similar cavity, which 

 he terms the temporal cavity, occurs in Amia between the bones and 

 the primordial cartilage, is widely open behind, and contains a por- 

 tion of the lateral musculature. In all probability the cavity in 

 Amiurus is a rudiment of this temporal cavity of Amia, the original 

 contents of which have vanished, their place being taken by fat and 

 blood-vessels. 



The same author suggests that the occipital segment of the Teleosts 

 has fused with it a certain number of vertebrae. He bases his asser- 

 tions on the presence of such vertebrae, partially fused, in Amia, 

 Polypterus, Protopterus and Lepidosteus. If such be the case, there 

 is no trace of such a coalescence in Amiurus. A nerve certainly 

 does pass out from the exoccipital behind the vagus, but in all its 

 relations it is a spinal nerve, passing through the arch of the pre- 

 ceding vertebra, as do the succeeding nerves. The occipital segment 

 is certainly composed of many segments, one corresponding to each 

 branchial branch of the vagus and to the glossopharyngeal, but 

 beyond these there is no indication of any further segments in the 

 basioccipital of Amiurus. 



II.— P ALATO-QUADRATE AND MANDIBULAR APPARATUS. 

 Under this head will be included a description of the maxillary 

 and palatine apparatus, as well as of the chain of bones constituting 

 the first postoral arcade, or, according to views expressed elsewhere, 1 

 the third cranial arcade, the trabecular cranii being considered as 

 representing the first arch, and the palatine as the second. 



1. The Premaxill^e, (PI. II., Fig. 1, Pmx.) 



Each is a small, somewhat arched bo'ne, supporting five or six rows 

 of teeth. They meet in the middle line, but are not united by suture. 

 The upper surface of each bone rests on the under surface of the 

 mesethmoid, and at the outer extremity each articulates with the 

 maxilla. 



2. The Maxilla, (PI. II., Fig. 1, Mx.) 



Depart very widely from the typical form. They are very much 

 elongated rods, projecting at right angles to the sides of the skull, 



1 On the Osteology and Development of Syngnathus Peckianus.(Storer). Quart. Journ. Micr. 

 Sci., N. S., Vol. XXIII., 1883. 

 21 



