THE COELOM, DIGESTIVE, AND RESPIRATORY SYSTEMS 175 



a tube, the cloaca, which proceeds dorsal to the girdle to the anus. At the point 

 of entrance of the large intestine into the cloaca the urinary bladder will be 

 found attached to its ventral surface by a stalk. On each side of the stalk of 

 the bladder, in females, a large white oviduct will also be seen entering the 

 cloaca. 



The female reproductive system may be noted at this time; that of the male 

 is so inconspicuous that it will not be described at this point. The ovaries are 

 a pair of large saclike bodies containing in their walls eggs of various sizes. 

 Each ovary is attached by its mesentery, the mesovarium, to the dorsal body 

 wall. Lateral to each ovary runs the oviduct, a large coiled white tube. It is 

 supported by the mesotubarium. 



3. The respiratory system. Pry open the jaws of the turtle and cut through 

 the angles of the jaws, cutting nearer the lower than the upper jaw. The anterior 

 portion of the cavity thus revealed is the oral or mouth cavity; the posterior 

 portion, the pharynx. The oral cavity is bounded by the jaws which have no 

 teeth but are clothed with horny beaks of epidermal origin. These beaks extend 

 as plates into the mouth cavity. In the roof of the mouth cavity posterior to 

 the plate is a pair of elongated openings, the posterior nares. Probe them and 

 determine that they connect with the anterior nares by passages which run 

 through the nasal cavities. The floor of the mouth cavity is occupied by the 

 fleshy pointed tongue. 



In the pharynx note that neither gills nor gill slits are present, although, as 

 we shall see shortly, the gill arches are represented. Behind the base of the 

 tongue is an elevation, the laryngeal prominence, in the center of which is an 

 elongated slit, the glottis. Feel the pair of small arytenoid cartilages, one on each 

 side of the glottis; they are derived from one of the gill arches. On each side 

 of the roof of the pharynx posterior to the muscles which connect the skull and 

 lower jaw is the opening of the auditory or Eustachian tube, a canal which leads 

 from the pharynx to the cavity of the middle ear. (The opening may have been 

 destroyed in cutting the jaws apart.) The auditory tube and also the cavity of 

 the middle ear are outgrowths from the first visceral pouch. Posteriorly the 

 pharynx narrows into the esophagus. 



Cut through the skin in the median ventral line of the neck and peel away 

 the skin from neck and throat. Separate the muscles in the median line of the 

 neck and find a tube stiffened by rings of cartilage. This is the trachea or wind- 

 pipe. Trace it forward until it disappears into the pharynx. In front of this 

 place note" the hard body of the hyoid, and by cleaning away muscles find also 

 two pairs of horns of the hyoid extending posteriorly. The hyoid and its horns 

 are derivatives of the second, third, and fourth gill arches. Open the mouth and 

 make a cut around the laryngeal prominence, freeing it from its position on 

 the dorsal surface of the body of the hyoid. The structure thus freed is the 

 larynx, an expanded chamber at the anterior end of the trachea. Find in the 



