982 W. K. GREGORY REPORT OE COMMITTEE ON NOMENCLATURE 



Hplieiiethmoid, which is a rather general ossification of the cartilages ol: 

 the front of the brain-case and the back of the nasal capsule, to include 

 a large ossification in the septum. 



This is my justification for styling the bone surrounding this anterior 

 end of the brain in Pariasaurus, sphenethmoid. 



The pair of small cartilage ossifications in the anterior part of the 

 brain-case of Urodeles, commonly called orbitosphenoids, obviously corre- 

 spond with the hinder part of the frog's sphenethmoid, and broadly with 

 tlie alisphenoids of the crocodile and Professor Williston's lizard bone. 

 Ft is impossible to be certain of a strict homology with either, on account 

 of the very complete chondrification of the anterior part of the brain-case 

 in Amphibia and the lack of knowledge of the site and mode of ossifica- 

 tion of the reptilian bones. For similar reasons there can be no certainty 

 in their identification with the true mammalian orbitospheno/ds, although 

 the two bones are homologous in a general sense. 



Difficulty arises in the name to be applied to the ethmoid of the Dicy- 

 nodonts. This bone is very similar in its relations to the sphenethmoid 

 of Pariasaurus, and had perhaps best bear that name, but its lower septal 

 part, which forms a great deal of it, is homologous with the "ethmoid"' 

 of Diademodon, itself homologous with the mesethmoid of a mammal. 



Perhaps the best way is to use ethmoid as a general term for any carti- 

 lage ossification in the posterior part of the nasal and anterior cranial 

 regions ; to restrict ' sphenethmoid to bones which have ossified partly in 

 the nasal capsule and j^artly in the brain-case; and to use mesethmoid 

 for all ossifications of the nasal septum alone. A new term is then needed 

 for the "orbitosphenoids" of Urodeles. 



The Preparietal (E. T. Newton) of Dicynodonts and Gorgonopsids is 

 a membrane bone distinct from the sphenethmoid, and must be recognized 

 as a nomen conservandum. 



Petrosal. — ^The name Petrosal comes from the "petrous portion of the 

 temporal" of human anatomy, and really means that bone, less the tym- 

 panic and squamosal ; it is, in fact, identical with the periotic. 



If I understand rightly, Professor Williston wishes to use this as equiv- 

 alent to Prootic in reptiles.*' This usage seems to me undesirable for the 

 following reasons : 



The labyrinth of reptiles is included by three bones on each side : the 

 paroccipital, which surrounds the posterior parts of the posterior vertical 

 and horizontal semicircular canals and the ])osterior parts of the vestibule, 

 sacculus, and lagena; the supi'aocci])ital, wliich siiri'onnds the upper parts 



« Spo Professor Williston's lator commenls below, p. 985. — Editor. 



