SCHl'LTK, SKI \VIIALE. 



Fig. ">. Thyroid r;irlilagi-. '1 / lut. size. 1, 

 Origin of thyrohyoidcus. 2, Origin of inferior 

 constrictor. 3, Insertion of sterno-thyrnideus. 

 4, Insertion of eirco-thyroideiis. .",. Origin of 

 muscle of laryngeal pouch. 



there is a deep notch between the diverging borders. The rostral margin passes laterad and 

 rostrad in a slightly concave course to the anterior cornu, 

 which is but a pronounced angle at the junction of the 

 rostral and lateral borders. The caudal margin is deeply 

 concave between the great posterior cornu and a mesal 

 process which marks its junction with the median border. 

 To this process and the whole caudal margin is attached 

 the muscle of the laryngeal pouch (M. thyreo-arytenoideus, 

 Dubois '). The posterior cornu is rounded, directed caudad 

 with a mesal concavity and has a length of 11.5 mm. 

 Mesad it gives origin to the crico-thyroid, dorsad to the in- 

 ferior constrictor. The thyro-hyoid arises from the anterior 

 cornu, the lateral half of the rostral border and the adjacent 

 ventral surface. The sterno-thyroid has a wide insertion 

 into the ventral surface and lateral margin in the angle 

 between the attachments of the thyro-hyoid and inferior constrictor muscles. 



Laryngeal sac. The laryngeal sac in this foetus has a length externally of 18 mm., a breadth 

 of 1 1 mm. Its wall is very thick, its lumen a transverse slit. This has an elongated communi- 

 cation with the larynx through the gap in the cricoid and between the bases of the arytenoids. 

 Its dorsal wall is attached in its whole length, rostrad to the cricoid, caudad to the tracheal rings, 

 so that its fundus is not free as in Dubois's figure of Balaena. This connection is by muscular 

 fasciculi. The muscle of the pouch, which Dubois considers to be the thyreo-arytenoideus 

 on account of its innervation by the inferior laryngeal nerve, arises from the caudal margin 

 of the thyroid cartilage and the ventral borders of its posterior cornua in their whole length. 

 The superficial fasciculi radiate from the mesal process of the cartilage; the rostral are trans- 

 verse and disappear beneath the cricothyroid muscles; the intermediate are oblique and turning 

 round the sides reach the cricoid cartilage; the caudal are nearly longitudinal and insert upon 

 the rings of the trachea as far caudad as the origin of the right eparterial bronchus. While many 

 surmises have been made as to the function of this sac, I do not remember to have seen it sug- 

 gested, that by its contraction and relaxation during submergence, a circulation of air in the 

 wide trachea and bronchi might be set up, which would favor the absorption of oxygen by bring- 

 ing the air in these passages more rapidly into contact with the respiratory membrane than 

 could be done by the usual diffusion currents. 



Trachea. The trachea is short and wide; dorsally it is flattened against the oesophagus. 

 Its external dimensions are as follows: length 9.5 mm.; breadth, rostral to right apical bronchus, 

 9 mm.; caudal to same 8 mm.; dorsoventral diameter 6 mm.; length to origin of right apical 

 bronchus, 6 mm. As in the other members of the order, the cartilaginous wall is very com- 

 plete, the rings being close-set and separated only by narrow intervals. The rostral ones as 

 Dubois - and Muller 3 have observed are continuous with the lamina of the cricoid cartilage. 

 Yentrally the ends of these rings are widely separated, the wall being completed by membrane. 

 This condition obtains in almost the whole extent of the laryngeal sac. Rostrad the membrane 



1 Dubois, Bug. In Weber's Studien fiber Saugethiere, II, p. 101 D. Jena, 1886. 

 - Dubois, E., op. cit., p. 92. 

 3 Muller, O., op. cit., p. 197. 



Oj- I HE 

 H UNIVEKi 



Vv OH 



