142 Mr. W. K. Parker on the Batrachian Skull [Dec. 16, 



which carries both the mandible and the hyoid arch in most fishes — sharks, 

 rajs, ganoids, and teleosteans. 



This part, the " hyomandibular," belongs to the second or hyoid arch, 

 and has no representative in most of the Sauro-batrachia, nor in the Ba- 

 trachia during their larval state. 



In Proteus, however, contrary to what is seen in the other tailed forms, 

 the proximal hyoid element is as massive as the mandibular pier, its 

 immediate "serial homologue." This "hyomandibular" of Proteus is 

 attached by ligament to the suspensorium, the stapes, and the auditory 

 capsule ; it is not tilted upwards and forwards like its counterpart in the 

 skate or osseous fish, but agrees with that of the shark in being directly 

 articulated to the cerato-hyal. This, however, does not take place by 

 direct superposition; but the hyomandibular is bevelled largely on its 

 inner face, and overlaps the cerato-hyal. Had it been tilted upwards and 

 forwards it would have applied itself to the outer face of the suspensorium 

 in the manner of the flat fore end of the Batrachian " columella," the 

 extrastapedial. 



Such a structure occurring in some low-generalized tailless amphibian 

 could only be interpreted as the lump of organic clay out of which the 

 columella had to be fashioned. 



Every anomaly in a frog or toad that shows how thin the middle wall 

 of partition is between the two groups will increase to me the probability 

 that the hyomandibular of the Proteus is the Batrachian columella " writ 

 large " *. 



On signs of Vertebral Segmentation seen in the cephalic part of the 

 Notochorcl. 



In my paper on the skull of the fowl (plate 82. fig. 3. nc) I have 

 figured the notochord in the third stage as having three partially formed 

 segments. The most distinct of these is the hindermost, and it is ossified. 

 That osseous tract is the homologue of an early vertebral " centrum ; " 

 and if the other two spindle-shaped regions were to ossify separately 

 there would be three rudimentary cranial centra. 



In toads of the first summer (sixth stage of this paper) the shrinking 

 notochord has become submoniliform, as in the chick, but it does not 

 ossify. 



In the Salamandrian Amphibia, however, the notochord acquires a 

 bony sheath in front ; and in Seironota perspicillata larvae half an inch in 

 length show two very well marked cranial centra, the front one with a 

 perfect osseous sheath, whilst the hinder segment has bony grains 

 scattered over the notochordal sheath. This last has the hourglass- 

 shape, and corresponds accurately in form with the rudimentary centrum 

 of the first cervical vertebra. 



The dorsal ends of the trabecule occupy the apex of the notochord, and 

 * It is small in Spelerpes and Desmognathus. 



