400 DA VI SON. [Vol. XI. 



is perfectly formed in cartilage. The squamosal is the only 

 otic element entirely ossified. A thick plate of basioccipital 

 cartilage lies beneath the hinder portion of the brain. The 

 parasphenoid forming the floor of the brain-case is somewhat 

 convex in its anterior part, but markedly concave in the pos- 

 terior region. The lateral walls of the brain-case in the pitui- 

 tary region posterior to the orbitosphenoid are of cartilage, as 

 in the adult. The other features of the cranium are so similar 

 to the descriptions of Hay and Kingsley that I deem it useless 

 to give them. 



The Visceral Skeleton. 



The mandible is quite the same as in the adult. The rami 

 are united anteriorly by strong connective tissue. Meckel's 

 cartilage lies in the groove of the ramus as far forward as the 

 point just below the eye, and extends backwards so far as to 

 be in contact with the quadrate. The dentary and angular are 

 well ossified. The teeth are fully developed. The hyoid appa- 

 ratus is unlike either the adult or Hay's embryo. It is for the 

 most part cartilaginous. The middle third of the basibranchial 

 appears quite well ossified. Thin parostoses invest the cera- 

 tohyal and ceratobranchial. The following elements compose 

 the apparatus : one basihyal, two hypohyals, two ceratohyals, 

 one basibranchial, two ceratobranchials, and eight epibranchials. 

 Hay found no basihyal in his embryos. A distinct nodule of 

 cartilage is present at the juncture of the hypohyal and cerato- 

 hyal on the external side. Its significance is unknown to me. 

 The ceratohyals extend outwards rather than backwards, as in 

 the adult. The larynx is an exceedingly simple structure, con- 

 sisting of a fibrous connective tissue tube, strengthened by 

 two lateral bars of cartilage. The external orifice is a longi- 

 tudinal slit. The trachea has no rings or partial rings of 

 cartilage. 



Soft Parts of the Head. 



The disposition of the muscles is approximately the same as 

 in the adult, with the exception that the place of the temporo- 

 cervical tendon appears to be filled by muscular tissue. Ven- 



