48 MAMMALIA. 



lages, especially in the male sex, as well as by a greater sexual dif- 

 ference, the female larynx being softer in its cartilages, smaller, and 

 less prominent. 



Singular varieties have still to be mentioned in the structure of 

 the larynx in some Mammalia, namely, among the Apes. In the 

 Sapajous the cavity of the larynx above the inferior chordae vocales 

 is lengthened out into a bent tube, the anterior wall of wV 

 formed by the thyroid cartilage, the superior by the epiglottis, the 

 posterior and inferior wall again by the adjacent prominences of the 

 cuneiform cartilages. Still more striking is the arrangement in the 

 Howling Apes, where membranes, bones, and cartilages, both of the 

 larynx and os hyoides concur to form the lateral laryngeal sacs or 

 apparatus of resonance, by which the volume of their voice is pro- 

 digiously increased. Even in the Orang-utang and Chimpanzee the 

 lateral ventricles of the laryngeal cavity are lengthened out into mem- 

 branous sacs, which extend forward beneath the body of the hyoid 

 bone. Similar sacs also occur in other Apes, as in the common 

 Inuus ecaudatus, where there is, however, only one' which opens by 

 a small simple orifice beneath the epiglottis above the lateral ventri- 

 cles. There is a remarkable valve, found hitherto only in the Mar- 

 mots, which, directed downward, can fill up and close the whole 

 breadth of the larynx. 



There is very generally situated upon and beneath the larynx in 

 the Mammalia a Thyroid gland. It consists in a great number of 

 two completely separated lateral lobes, and, as a rule, is double. In 

 many Apes both lobes are more separated than in Man, but usually 

 united by a ligament. Both halves of the gland lie very far apart in 

 the Otter, where they are situated upon the sides of the larynx, and 

 are in contact with the sub-maxillary glands. In the Cetacea, on the 

 contrary, the flat or heart-shaped thyroid gland is not separated into 

 two lobes, and lies transversely over the trachea. 



The Trachea in the Cetacea is extremely short, on account of 

 the shortness of the neck, and, at the same time, very wide ; the 

 cartilaginous rings are very closely approximated together, and in 

 the Whales not closed anteriorly, so that here it is membranous. 

 In the herbivorous Cetacea it is not divided into separate rings or 

 arches, but is wound about by a spiral band of cartilage. In the 

 Horse and some Ruminantia it consists of complete rings, while in 

 a large number of animals it is perfectly membranous behind, as ap- 

 pears to be particularly the case in the Rodentia. The number of 

 rings varies remarkably, and is determined by the length of the 



