NECTtJRUS MACULATtJS. 423 



open gill slits guarded by rudiments of gill rakers, much as in the Axolotl, and as these 

 occur, the one between the first and the second arches, and the other between the second 

 and the third, and consequently in the intervals between the integumental branchiae, the 

 suggestion of connection l)etween the two systems is still more misleading. It may be 

 remembered in this connection that there is a similar external gill upon the shoulder 

 girdle in the Dipnoan, Protopterus, the relation of the two being wholly topographical 

 and without morphological significance. Hence the physiological moments which have 

 develojjed the external branchiae in this place are plainly the utilization of the gills and 

 their muscular mechanism for support and motion, as well as the currents of fresh water 

 which can be driven through the gill slits in such a way as to bathe the respiratory 

 fringes. 



Since the attempt of Fischer ('64) to account for a fourth branchial arch by supposing 

 that the first consists of two fused arches, no good suggestion concerning branchial arches 

 posterior to the third had been made up to about ten years ago, since when a series of 

 investigations by Gegenbaur (29'). Goppert ('94), and myself ('92), have rendered it 

 probable that the larvugo-tracheal cartilages of Amphil)ia are modified portions of the 

 fifth arch, pei-haps the epiln-anchials. A fourth arch, attached to the hyobranchial 

 apparatus, is present in several of tlie lower Urodeles, (Siren, Amphiuma, Crypto- 

 branchus) , and its apparent absence in Necturus has awakened some little speculation. 

 The rudiment of this was finally discovered by Goppert, who found it to consist of a 

 raphe of connective tissue, separating two muscles normally belonging to the branchial 

 system, and in which, in the larva, he discovered a few cartilage cells. This view I can 

 corroborate by investigations upon the same point at the same time, and which had led 

 me independently to the same conclusions previous to the appearance of the work of 

 Goppert. This raphe is given in the figiu'e referred to (pi. 65, fig. 12), and there can now 

 be little doubt that it represents the missing fourth epibranchial. Concerning the struc- 

 ture of the metamorphosed fifth In-anchial arches (laryngo-tracheal cartilages) , they con- 

 sist normally of a single pair of somewhat curved pieces, applied to the sides of the glottis 

 and short trachea, and were first described by Henle under the name of cartilago laterahs. 

 They are individually very variable and often have notches, foramina, or detached pieces, 

 but consist essentially of an anterior flat piece in the form of a triangle, from the poste- 

 rior internal angle of which depends a curved tracheal process extending posteriorly. A 

 more careful description of these cartilages and figures of several varying forms are given 

 in the author's article on the amphibian larynx ('96) • 



Suspe7isorUtJ relations of the hyoid. — Tiie distal end of the ceratohyal enters into a 

 ligamentous connection with various parts of the skull and mandible and thus bears a 

 close relation to the suspensorial apparatus of the mandible, a region which has such an 



