84 ME. W. a. EIDEWOOD OIN" THE HTOBEAB'CHIAL 



petroLyoideus, and the liyoglossus are considerably reduced. 

 The most remarkable feature is, without doubt, the extensive 

 development of the dilator (PL 10. figs. 3 & 4, d). This muscle 

 covers the whole o£ the sides of the laryngeal complex, nearly 

 the whole of the ventral surface, and a considerable portion of 

 the dorsal. It is distinctly differentiated into a superficial and a 

 deeper layer (d and d'), and the tendon of the latter passes for- 

 ward and inward in the pulley-like groove at the side of the 

 roof of the larynx, and is inserted into the dorso-external border 

 of the posterior massive part of the arytenoid. The aponeurosis 

 that passes over the blinker-shaped process of the laryngeal 

 cartilage is very delicate, far more so than in the female. The 

 dilator muscle in the female extends round the outer border of 

 the thyrohyal and very slightly, if at all, on to its ventral surface ; 

 but in the male the belly o£ the muscle has spread so as to cover 

 the whole of the ossified part of the thyrohyal and to meet its 

 fellow of the opposite side in the ventral median line (see PI. 10. 

 fig. 3). The only parts of the ventral surface of the larynx over 

 which the muscle does not extend are, first, a small triangular 

 area in front occupied by the hyogiossus, and, secondly, a larger 

 space, also triangular, at the posterior end between the petro- 

 hyoids. 



The dilator anterior (PL 10. fig. 4, d.a.) is better differentiated 

 from the dilator than in the female, although relatively shorter 

 and smaller in bulk. Its fibres are inserted into the arytenoid 

 cartilage over the anterior two-thirds of the side of the glottis. 

 They pass outward and downward, but very slightly backward, 

 and spread out in the form of an aponeurosis over the ventral 

 surface of the anterior part of the dilator. Wilder (43. Taf. 21. 

 fig. 61, t) identifies this muscle as the " dilatator laryngis." He 

 describes it, however, as arising from the thyrohyals, an origin 

 peculiar to the female ; and I cannot help thinking that he was 

 mistaken in the sex of the animal he examined. The hyogiossus 

 (PL 10. fig. 3, Ji.i.) is much more feebly developed than in the 

 female, and although the relations of the anterior end are the same, 

 the posterior extremity does not reach nearly so far back. In the 

 female the outer fibres arise from the thyrohyals, but in the male 

 the whole of the muscle arises from the cartilage of the laryngeal 

 floor. The reduced hyogiossus thus probably corresponds with 

 the median belly only (hyogiossus internus) of the muscle in the 

 female. The geniohyoideus internus (PL 10. fig. 3, g.i.) is more 



