32 BULLETIN 34, UNITED STATES NATIONAL LIUSEUM. 



lu tlieilevelopmeot of tbe vertebiieallaro first biconcave, or ILsh-like. 

 The intervertebral cartilage ossifies later, and attaches itself to the 

 centrum posterior to it, forming an opistboccelous articnlatiou. There 

 are uo procoelous vertebrpe among Urodela. 



The feet are first simple at the extremity (Plate 20, fig. 0), but soon 

 become bifurcate (Fig. 5), or with two digits. This was first observed 

 by Eusconi in 1821 in the European Ilemisalamandra cristata. Pro- 

 fessor Baird* fii^st observed this in the Ambhj stoma imnctatum in larvae 

 of 1.4™"^ iu length. The same has since been observed by myself in 

 18G9,t ami later by Gotte| iu his essay on the development and re- 

 generation of the foot-skeleton in the triton; also by Strasser and 

 by Hoy. In AmbJystoma imnctatum the numbers of digits succeed 

 each other as follows : First stage, 2 before, hind limb none; second, 

 3 before, hind limb noue ; Ihird, 3 before, hind limb 2; fourth, 3 be- 

 fore, hind limb 3. Sometimes the anterior digits are complete in iium 

 ber before the posterior foot appears, and we have combinations of 

 numbers from 4—0 to 4 — 3, and 4— 4 to the full number, 4 — 5, which is 

 luund in alt specimens of 2.5™'" and upwards. 



As already observed, the Batrachia are supposed to have been de- 

 rived from the Dipnoi. Spicimens of Lepidosiren annectcns have been 

 described § which have the extremity of the limbs abnormably bifur- 

 cate, but the abnormality is perhaps in the direction of the evolution of 

 digits. Dr. G. Baur believes that tlie third, fourth, and fifth digits have 

 grown or sprouted successively in time from the external distal angle of 

 the ulna and fibula, while the first and second are represented by the 

 two original branches. || 



In the cranium a good many important changes occur before the bcnes 

 appear,^] Among the first of these is the division of the five simple 

 transverse branchial cartilages into two segments each, epibranchials 

 and ceratobranchials, or, in the case of the anterior arch, into cerato- 

 hyal and hypohyal. So the mandibular cartilage immediately anterior 

 to the ceratohyal, divides into the superior quadrate, and the inferior 

 meckelian or mandibular. A subsequent change is the fusion of the 

 quadrate cartilage at its superior end with the trabeculum of its side, 

 and with the pterygopalatine arch with the inferior end. (See Plate 4S, 

 figs. 7-9 ) At this time the chordadorsalis has retreated till it is only 

 present between the esoccipital cartilage below. When ossification com- 

 mences, the vomers, palatines, and pterygoids are all distinct. Towards 

 tiie end of the metamorphosis the former two unite, and the pterygoid 

 separates from the palatine. Both these elements contract away from 

 each other until they are widely separated, and the pterygoids are much 



*Iconograpliic Eacyclop;udia, 1851. 

 t Proceedings Phila. Acad., j). 95. 

 t 1879. 



^^ By Steindacliner. 



II Beitrligc zur Morpliogeuie d. Carpus-ii. Tarsus dor Vertebraten, 1887, p. 67. 

 HThe facts as to the first stages of the skull of the iarva of Amblystoma are derived 

 from Dr. W. K. Parker, PbilosopL. 'I'ransac 1877, p. 52'J. 



