48 LABORATORY DIRECTIONS 



shark, bear no gill filaments; the gills are external in position. 

 Find the opening into the oesophagus. On the floor of the 

 pharynx just anterior to the opening to the oesophagus is a tiny 

 slit, the glottis, which leads to a small, very primitive larynx. 

 The glottis is supported by two very small arytenoid cartilages, 

 probably derived from the seventh visceral arch. The larynx 

 is joined to the lungs by a short trachea. Slit open a lung and 

 observe that the interior surface is smooth. This is a primitive 

 condition. 



Necturus has three methods of obtaining oxygen: through 

 the gills, through the skin, and through the lungs. When using 

 the lungs air passes through anterior nares, nasal passages, 

 posterior nares, mouth cavity, pharynx, glottis, larynx, trachea 

 and lungs. 



Digestive and Respiratory Organs of the Cat 



Remove the skin and superficial fascia from the head and 

 neck. On either side of the neck lies the large external jugular 

 vein. Trace it toward the head. At about the angle of the 

 jaw it will be seen that the external jugular is formed by the 

 confluence of two large veins: the posterior facial bringing blood 

 from muscles and glands in the region of the ear, and the anterior 

 facial returning blood from the face and tongue. A communi- 

 cating branch connects the anterior facials of the two sides. 

 A pair of lymph glands lie along the anterior facial near its 

 union with the posterior facial. These may be removed. 



Salivary Glands. — Remove the skin and superficial fascia 

 from the head and neck. There are three important salivary 

 glands which empty their secretions into the mouth cavity. 

 The parotid gland, the largest of the salivary glands, is a large 

 lobulated mass at the base of the ear. Trace its white duct 

 (Stensen's duct) across the surface of the large masseter muscle 

 to the corner of the mouth, where it opens near the last premolar 

 tooth. The submaxillary and sublingual glands lie under the 

 posterior angle of the jaw, somewhat deeply embedded. Do not 

 mistake the two lymph glands on the surface for them. The 

 duct (Wharton's duct) of the submaxillary gland extends along 

 the under side of the mandible and opens on the floor of the 

 mouth just back of the incisor teeth through a small papilla. 



