MAMMALS. 587 



noticed, but a branch of tlie external carotid also, the ophthalmic 

 artery, forms in the ruminants and the cat a vascular plexus in the 

 orbit \ and a few years ago Hyetl discovered in the hog and the 

 ruminants, wonder-nets in the nasal cavities, formed by the sphe- 

 nopalatine artery^. Conspicuous vascular plexures occur also in the 

 dolphins on the intercostal arteries and the iliac veins''. 



The respiratory organs are distinguished by the minute division 

 of the bronchial tubes. The pulmonary vesicles are in immediate 

 connexion with the delicate terminal branches of these tubes, and 

 may, in contradistinction to the air-cells of reptiles, be named 

 tei'minal cells, although the idea can no longer be maintained that 

 every terminal branch of the hroncJii forms by its blind extremity 

 a single pulmonary vesicle. Air-sacs in connexion with the lungs, 

 as they are observed in birds, are not present in the class of mam- 

 mals. In most mammals the cartilaginous rings of the trachea 

 do not form a complete circle, but leave an interspace on the pos- 

 terior surface. In the dolphins, however, and some other mammals 

 the rings are more perfect; in the whales the rings, according to 

 the investigations of Gr. Sandifort*, are interrupted by a mem- 

 branous portion on the anterior surface ; a peculiarity by which 

 the wind-pipe of these animals is distinguished from that of all 

 other mammals. Curvatures in the trachea have been observed 

 in the three-fingered sloth alone, where the wind-pipe descends 

 nearly to the diaphragm, and then curves upwards again before it 

 divides into the two bronchi. As a rule tliere are two bronchi, one 

 for each lung, although in the ruminants, the dolphins, and some 

 other mammals, a third smaller bronchial tube occurs, which arises 



1 Rapp, Meckel's Archiv, 1827, s. 8.. 9 ; in the cat, figxired by Otto, in Carus 

 1. 1. Tab. VII. fig. 4. 



2 Beitrdge zur vergleichenden Angiologie. Wien, 1 849. 



3 Von Baer Nov. Act. Acad. Cces. Leap. Car. Vol. xvii. P. i. pp. 393—408 ; 

 Beeschet Histoire anatomique et liliyslol. d'un organe de nature vasculaire chez Its 

 cetaccs, Paris, 1836, 4to, avec pi. Comp. on the arterial system in general of mam- 

 mals Barkow Bisquisitiones circa originem et dec^irsxmi arteriarum Mammalmm, 

 Accethnit Tab. sen. iv. Lipsiae, 1829, 4to, and by the same, Bisquisitiones receniiores, 

 &c. in Nov. Act. Acad. Cces. Leop. Car. Vol. xx. P. 2, 1843, pp. 607 seq. 



^ Bijdragen tot de ontleedhmdige Icennis der WalvisscJien, Nieuwe Yerhandelingen 

 der Eerste Klasse van, het KoninU. Nederl. Instituut, iir. Deel, 1831. — Besides the 

 general works on comparative anatomy (particularly the new edition of Cuvieb, by 

 DuvEENOY and Meckel, System der vergl. Anat. vi. s. 364 — 474) on the respiratory 

 organs of mammals may be consulted with advantage : A. Lerebodllet Anat. comp. 

 de Vappareil respiratoire des animmix vertehres, Strasbourg, 1838, 4to, pp. 24 — 42. 



