SKELETON AND LiKYNX OF XEN"OP[JS AKD PIPA. 83 



the ala of the hyobraucliial skeleton, at about the level o£ the 

 anterior ends of the thyrohyals, in the position marked g.e. in 

 fig. 1, PL 8. This external geniohyoid of Xenopus is called by 

 Mayer (36. p. 30) the genioceratoideus, but he considers it 

 homologous with the muscle which he had previously named the 

 geniohyoideus in Pipa (25. p. 538). The geniohyoideus internus 

 (PI. 10. fig. 1, g.i.) (geniohyoideus of Mayer, 26. p. 30) is attached 

 by its anterior extremity to the mandible, nearer to the symphysis 

 than the externus, runs parallel with the latter and extends 

 backwards below the larynx to be inserted into the ventral surface 

 of the posterior epiphysis of the thyrohyal. It runs ventral to 

 the hyoglossus, but dorsal to the petrohyoideus. The two internal 

 geniohyoid muscles are in close contact with one another for the 

 greater part of their length, but they diverge somewhat pos- 

 teriorly. In the frog, the geniohyoideus has a single belly in 

 front and divides posteriorly into two parts. The internal of 

 these (geniohyoideus medialis of "Walter, 40. p. 32) is attached 

 to the inner border of the anterior end of the thyrohyal, and 

 the outer (g. lateralis of "Walter, 40. p. 33) to the hinder of the 

 two lateral cartilaginous processes of the body of the hyoid. 

 If vi^e admit that these two divisions of the muscle correspond 

 with the geniohyoideus internus and externus respectively of 

 Xenopus, a perfectly legitimate supposition, we must not fail to 

 notice that the internal division is attached in Xenopus to the 

 posterior epiphysis of the thyrohyal, but in the frog to the 

 anterior end of that bone. 



Ohliquus internus. — The anterior end of the internal oblique 

 muscle, though inserted mainly into the Tentral surface of the 

 great wing of the hyobranchial skeleton, sends a small slip with 

 tendinous extremity to the posterior end of the thyrohyal (PI. 10. 

 fig. 2, 0.?'.). The incorporation of the thyrohyal into the laryngeal 

 complex of Xenopus demands that this slip should be regarded as 

 a laryngeal muscle, and a passing notice is therefore here accorded 

 to it. 



Male. 



In considering the muscles of the male Xenopus, it will be 

 sufficient to note only those points in which they difi'er from the 

 muscles of the female. The same seven muscles are in relation 

 with the larynx, although they are very much modified in form. 

 The trend of such modification is not in one uniform direction, 

 for, while the dilator muscles are excessively enlarged as com- 

 pared with those of the female, the geniohyoideus internus, the 



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