In the fish and toad, already studied, the head is closely joined to the trunk. How is it with the bird? Observe that the knee of the sparrow is covered by feathers and that it is the ankle which extends down as the bare unfeathered part to the digits. How many digits have the feet of the bird? How are they arranged?

Internal structure (fig. [132]).—Technical Note.—With a pair of scissors cut just beneath the skin anteriorly from the cloacal opening to the angle of the lower jaw. Pin the sparrow on its back by the wings, feet, and bill. Push back the skin from both sides and pin out.

Fig. 132.—Dissection of the English sparrow, Passer domesticus.

Note the large powerful pectoral muscles. Note a hard median projection of bone, the sternum, which is a large keel-shaped bone with lateral expansions to which are attached the ribs. Where are the largest and most powerful muscles of the toad located? Where are they in the fish? In the bird the most powerful muscles are these pectoral muscles, which move the wings in flight.

Technical Note.—Cut the pectoral muscles from the left side of the sternum, push back and pin to one side. With a strong pair of scissors cut through the ribs on the left side of the sternum and through the overlying bones. Lift the whole sternum, with the right pectoral muscle attached, to the left side of the pan and pin it down. Cut through the membrane which covers the viscera and cover the dissection with water.

In this operation note the V-shaped wishbone in front of the sternum. It is composed of the two clavicles with their inner ends fused. Note the stout coracoid bones extending from the anterior end of the sternum to the shoulder.

Note near the middle of the body the heart with the large blood-vessels proceeding from it. Behind the heart lies the large reddish-brown liver, and on the left side below the liver is the large gizzard or muscular stomach. Note the viscera folded over themselves in the body-cavity. Push them temporarily aside and note in the dorsal region under the heart large pinkish spongy sacs, the lungs. These are attached by short tubes, the bronchi, to the long cartilaginous trachea. At the union of the bronchi with the trachea is a small expansion with cartilaginous walls, within which are stretched small bands of muscles. This organ is the syrinx, the song- or voice-apparatus of the bird. It should be cut open and carefully examined. Trace the trachea forward to its anterior end. It opens by a glottis into the larynx, a slightly swollen chamber with cartilaginous walls. Note the U-shaped hyoid bone surrounding the front of the glottis. Through a blowpipe or quill inserted into the glottis blow air into the trachea and observe the inflation of the lungs and of certain large air-sacs in the abdomen, which communicate with them.

Beneath the trachea note the long œsophagus. Inflate the œsophagus with a blowpipe and note how distensible is its lower end near the breast. This distensible portion is called the crop. If the alimentary canal be drawn out straight the œsophagus will be found to run as an almost straight tube down the left side of the body to the gizzard. This latter organ has very thick muscular walls and in it the food is ground up among the small bits of gravel it contains. Extending from the gizzard near the entrance of the œsophagus note the long pyloric loop of the intestine called duodenum. Within this loop is a long pinkish gland, the pancreas, which empties by a duct into the duodenum. Into the duodenum also the overlying liver empties its secretion of bile from the median-placed gall-bladder. From the duodenum the small intestine or ileum extends with many convolutions to its exit through the cloacal aperture. On the intestine near the cloacal opening note a pair of glandular structures, the cæca. The short part of intestine between the cæca and cloaca is called the rectum. On the left side of the body beneath the gizzard note a dark glandular structure, the spleen.