398 DR MORRISON WATSON AND MR ALFRED H. YOUNG 
as the pharnyx had been separated from the skull. These fibres pass backward 
on the side of the pharnyx, and become continuous with those of the opposite 
side behind that tube. They intermingle also with the fibres of the stylo- 
pharyngeus. The deeper fibres lie immediately under cover of the mucous 
membrane of the pharynx, and are most easily dissected from the inside of the 
tube. They form a constrictor or sphincter of the spiracle, and surround that 
cavity almost to its external opening. They are aggregated so as to form a 
muscular ring of great strength which surrounds the lower aperture of the 
spiracle. In other words, we have in these last mentioned fibres a means 
whereby the spiracular cavity may be shut off from the pharynx, whilst the 
upper fibres of the muscle may be regarded as being of service in producing 
alterations in the form and capacity of that chamber. 
The Middle Constrictor arises from the posterior border of the thyro-hyal 
bone. The fibres pass backward, and blend behind the pharynx with those of 
the superior and inferior constrictors. 
The Inferior Constrictor arises from the whole length of the superior border 
of the thyroid cartilage, including its posterior horn. It does not take any 
attachment to the cricoid cartilage. The fibres pass backward, and unite with 
those of the opposite side along the middle line posteriorly. A strong median 
raphé, to which the fibres of the constrictor muscles are attached, extends along 
the posterior aspect of the pharynx. 
Stylo-pharyngeus Muscle arises from the base of the stylo-hyal bone. The 
fibres ascend obliquely upward and forward, and blend with those of the 
superior constrictor. It is a strong riband-like muscle, and when in action pulls 
the bag of the pharynx backward. : 
Palato-pharyngeus Muscle.—This muscle, which is described by both Murtz* 
and Macatistert in Gilobiceps, could not be distinguished by us in Beluga. 
The arrangement of the pharyngeal muscles above described closely re-— 
sembles that observed by MacauisTErR{ in Globiocephalus. The deeper layer of 
our superior constrictor evidently corresponds to the constrictor of the posterior 
nares of that author. According to him, in Globiocephalus the middle con- 
strictor arises as in Beluga from the thyro-hyal bone, whilst Dr Murie § found 
it arising from the thyroid cartilage. In Beluga the origin of the inferior con- 
strictor is confined to the thyroid cartilage, which is in accordance with Dr — 
Morie’s observations on G'lobiocephalus. MAcAuisterR, t on the other hand, 
observes that its fibres take an additional attachment to the cricoid cartilage 
in the latter species. Balenoptera rostrata || differs from both in the rudimen- 
tary condition of the superior constrictor. 
(Esophagus. —This tube measures 10 inches in length. Its mucous membrane 
* IL p. 254. + VL p. 480. + VI. p. 479. 
§ IL..p. 254, | I. p. 245. 
