SKELETON AND LARYNX OE XENOPUS AND PIPA. 87 



montory of the arytenoid, and by its dorsal surface to some of the 

 fibres of the dilator anterior. Posteriorly, the compressor muscles 

 of the right and left sides unite, immediately behind the glottis, 

 in a linea alba which extends backwards for a distance equal to 

 the width of each muscle. The anterior extremity of the com- 

 pressor is attached to the lateral edges of the median isthmus of 

 cartilage (PI. 9. fig. 1, i) which connects the part of the hyo- 

 branchial cartilage bounding the hyoglossal foramen with that 

 which forms the anterior end of the laryngeal complex. In this 

 respect the compressor differs from that of Xenopus, for in this 

 latter genus the attachment of the anterior end of the muscle is 

 to the dorsal surface of the equivalent cartilage. 



The hyoglossus [Laryngoglossus, Mayer, 35. p. 537 and fig. 2, e; 

 Biickwartszieher der Zunge, Meckel, 28. Theil iv. p. 340 ' 

 Hyoglossus, Henle, 19. Taf. 2. figs. 22 and 23, 4'\ is a much longer 

 muscle than that of Xenoj)us, and extends nearly the full length 

 of the larynx. The external and internal divisions also are better 

 difierentiated. The hyoglossus internus (PI. 10. fig, 6, A.«.) arises 

 from the ventral surface of the larynx near the posterior end, 

 and the area of attachment slopes obliquely backwards and out- 

 wards. The muscle crosses dorsally to the petrohyoideus and 

 runs forwards beneath the larynx, diminishing at the same time 

 in width. The internal hyoglossals of the right and left sides 

 converge anteriorly ; they fuse together, pass through the median 

 foramen in the hyobranchial skeleton, and spread out as a single 

 muscle (PI. 10. fig. 5, h.i.). This is inserted into that part of the 

 mucous membrane of the floor of the mouth which lies over the 

 beak or point of the hyobranchial skeleton (PI. 9. fig. 1, ch.'). 

 The external hyoglossus (PI. 10. fig. 6, Ji.e.) is in the main slightly 

 broader than the internal, but its posterior area of attachment is 

 smaller than, and lies posteriorly to, that of the latter. The two 

 muscles, internal and external, thus overlap one another at their 

 posterior ends, but they separate out anteriorly. The external 

 trunks occupy a lateral position with regard to the internal as 

 they pass through the hyoglossal foramen. Then, instead of 

 continuing forwards, they turn sharply outwards at right angles 

 to their former course (PI. 10. fig. 5, h.e.), the left to the left and 

 the right to the right. They spread out and become inserted 

 into the mucous membrane of the lateral parts of the floor of 

 the mouth. Henle (19. p. 25) mentions the three muscles 

 spreading out in the floor of the mouth, but he fails to note the 



