1 8 HAY. [Vol. IV. 



The hyobranchial apparatus (Figs. 4 and 5) consists of the 

 hyoid arch and four branchial arches. The hyoid arch presents, 

 on each side, a hypohyal and a ceratohyal. The basihyal has 

 not as yet become chondrified. There is a single basi-branchial 

 as in the adult. The four branchial arches are much as in the 

 mature animal. There is no second ceratobranchial present. 

 Huxley states that there is one present in the adult, but it 

 is not represented in Wiedersheim's figure. The ossification 

 connected with the hyobranchial arches will be referred to 

 immediately. 



Ossifications. — It has been already stated that the exoccipi- 

 tals are undergoing ossification. These ectostoses do not meet in 

 the lower middle line in front of the foramen magnum. 



The only other ossification of this kind occurs in the first 

 branchial arch. A delicate but easily distinguishable layer of 

 bone invests the slender portion of the lower end of the carti- 

 laginous bar, as shown in Fig. 5. 



The following parostoses occur in this skull : premaxillary, 

 vomers, parasphenoid, frontals, parietals, squamosals, dentaries, 

 angulars, and a hyoidean splint. In my determination of the 

 presence and the relations of these bones, as well as of the two 

 cartilage bones, I have carefully compared them with the ossifi- 

 cations found in the skulls of larval Afjtbly stomas. I have also, 

 in the case of nearly all of them, been able to dissect them out, 

 clean them, and apply chemical tests. 



The premaxillary of the adult is a very remarkable bone ; it 

 is no less so in the case of the embryo. In the adult the lat- 

 eral halves are so completely consolidated that no evidence is 

 afforded by them that they ever have been distinct. It is com- 

 posed of two alveolar processes : an ascending process, which 

 runs backward between the nasals and the frontals to a point 

 a little behind the line joining the anterior borders of the 

 orbits ; and a palatine process, which appears in the roof of the 

 mouth between the vomers nearly as far back as their hinder 

 ends and underlying the parasphenoid. It appears to be this 

 process which has been described by several authors as a sphe- 

 noidal ossification. For nearly half their length anteriorly these 

 two processes are connected by a thin plate of bone which 

 functions as a nasal septum. Nearly the whole remaining 

 space between them is occupied by cartilage. Dr. Wiedersheim 



