Jan., 1904.] Comparative Chart of Vertebrate Skull. 53 



The pterotic has been called the squamosal, but the latter arises 

 from a separate ossification and is not present in fishes. The tur- 

 binals are derived from outgrowths of the bones surrounding the 

 nasal chamber and represent true ossifications in Mammals, 

 but may remain cartilaginous in the lower groups. They are first 

 recognized in the Amphibians, where they are merel}' cartilagin- 

 ous protuberances on the bones of the floor and side walls of the 

 nasal chamber. 



Characteristics of the different classes : 



Fish. — One occipital condyle. Opercles present only in the 

 fish. Some fish have bones which are lacking in others, there 

 being a great difference between some of the families in this 

 respect. 



Amphibians. — Two occipital condjdes ; no trace of supra- or 

 basioccipitals. The skull is remarkable for the extent to which 

 the chondrocranium is retained and the consequent small number 

 of primary bones. The prootic alone forms the auditory capsule 

 in the frog, the other otic ossifications not being developed ; in 

 the Urodels an opisthotic is added. 



Reptiles. — One occipital condyle. The transverse is present 

 in all reptiles, except the turtles, and in no other vertebrates. 

 The zygomatic arch, formed by the quadrato-jugal and the jugal, 

 is wanting in the Ophidians. In turtles there are no teeth, and 

 the basisphenoid is the only one of the sphenoidal bones present. 

 Of the otic bones the prootic is always distinct, the epiotic is 

 fused with the supraoccipital, while the opisthotic (free in tur- 

 tles) is usually united to the exoccipital. 



Birds. — One occipital condyle. The bones of the cranium fuse 

 early .so that the sutures between them are obliterated. Teeth 

 are lacking in modern birds. The anterior end of the parasphen- 

 oid forms the rostrum and the posterior the basitemporal. 



Mammals. — Two occipital condyles. The lower mandible 

 articulates with the squamosal and is composed of five elements 

 on each side, as the articular has been taken into the middle ear 

 to form the malleus. The quadrate has gone into the ear and 

 become the incus. The stapes is derived from the hyomandibu- 

 lar and from some membranous elements. 



EXPL.\NATION OF PI,.\TES III AND IV. 



S=Salmon; F=Frog; U=Urodele; L=Lacerta; 0=Ophidian; T=Turtle; 

 A=Alligator ; D=Duck ; P=Pigeon ; C=Chicken ; H=Dog ; R=Rabbit ; 

 M=Man. In the first column after the name of the bone, c^cartilage bone 

 and m=menbrane bone. 



