ON THE ANATOMY OF THE NORTHERN BELUGA. 415 
surface of the thyroid cartilage. The posterior cornua of the thyroid are con- 
nected to the cricoid by means of strong capsular ligaments. 
The form of the erico-arytenoid articulation is such as to admit of rotation 
of the arytenoid upon the cricoid cartilage, the effect of rotation inwards being 
to approximate the inferior borders of the arytenoid cartilages in the centre of 
the larynx, thus giving rise to the formation of two distinct channels, such as 
have been described by Dr Muriez in Risso’s Grampus. 
The approximation of the inferior borders of the arytenoid cartilages is 
effected by the contraction of the thyro-arytenoid muscles. 
Muscles of the Larynx. 
Crico-arytenoidet postici are very strong ; they arise from the whole of the 
dorsal surface of the cricoid cartilage, and also from the tips of the posterior 
cornua of the thyroid; the fibres pass obliquely upwards and outwards, to be 
inserted into the outer extremities of the tuberosities of the arytenoid cartilages. 
Thyro-arytenoidei arise from the inferior mesial line of the thyroid cartilage, 
and are inserted into the inferior external angle of the arytenoid cartilage. 
Arytenoideus.—This muscle arises between the superior surfaces of the 
arytenoid cartilages ; it is limited to the basal third of these cartilages. 
Hyo-epiglottic muscles Dr Murise* describes as two in number. In Beluga 
the fibres are coalesced into a single muscular mass arising from the posterior 
borders of the cartilaginous cerato-hyals ; the attachment to the stylo-hyals, 
noted by Murte in Gilobiocephalus, does not exist in Beluga. The muscle is 
inserted into the posterior half of the lower surface of the epiglottic cartilage. 
Crico-thyroid are strong muscles, which arise from the outer surface of the 
cricoid cartilage. They separate as they pass forwards, and are inserted into 
the posterior border of the thyroid cartilage as well as into its posterior cornua. 
With respect to the action of these muscles, the arytenoid and posterior 
crico-arytenoid muscles separate the lower borders of the arytenoid cartilages, 
increasing thereby the size of the rima-glottidis, whilst the thyro-arytenoids act 
in an opposite manner. The hyo-epiglottideus raises the epiglottis, and the 
crico-thyroids approximate the cartilages between which they are placed. The 
presence of the last-named muscles in an animal, which, so far as we are aware, 
is not gifted with voice, shows that they have other and probably no less im- 
portant functions than that with which they are generally credited. 
A comparison of the muscles of the larynx of Beluga with those of other 
whales, shows a close resemblance between them and those of Globiocephalus 
melas,t and a corresponding deviation in both from the arrangement met with 
in Balenoptera rostrata.{ There are, however, two hyo-epiglottic muscles 
* II. p. 263 (Giobiocephalus melas). + IL p. 263. t L pp. 237, 238. 
