MAMMALS. 587 



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

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

 orbit 1 , and a few years ago HYRTL discovered in the hog and the 

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

 nopalatine artery 2 . Conspicuous vascular plexures occur also in the 

 dolphins on the intercostal arteries and the iliac veins 3 . 



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 

 terminal cells, although the idea can no longer be maintained that 

 every terminal branch of the bronchi 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 there 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 KAPP, MEOKEL'S Archiv, 1827, s. 8, 9; in the cat, figured by OTTO, in CABUS 

 1. 1. Tab. vii. fig. 4. 



2 Beitrdge zur vergleichenden Angiologie. Wien, 1849. 



3 VON BAEB Nov. Act, Acad. Cos. Leop. Car. Vol. xvn. P. i. pp. 393 408 ; 

 BRESCHET Histoire anatomique et pJiy&iol, d?un organe de natu/re vasculaire cJiez les 

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

 mals BABKOW Disquisitiones circa originem et decursum arteriarum Mammalium, 

 Accedunt Tab. sen. rv. Lipsi0e, 1829, 4to, and by the same, Disquisitiones recentiores, 

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



4 Bijdragen tot de ontlecdkundige fcennis der Walvisschen, Niemoe Verhandelingen 

 der Eerste Klasse van het Konirikl. Nederl. Instituut, in. Deel, 1831. Besides the 

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

 DUVEBNOY and MECKEL, System der vergl. Anat. vi. s. 364 474) on the respiratory 

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

 de rapparett respiratoire des animaux vertbres, Strasbourg, 1838, 4to, pp. 24 42. 



