THE ENGLISH SPARROW. 227 



Near its origin the aorta gives off a pair of large (in- 

 nominate) branches, which go to right and left sides of 

 the anterior part of the body. Each of these branches 

 divides into three smaller arteries (carotid, brachial, and 

 pectoral), corresponding to the three branches of each 

 prsecava. The aorta curves dorsally, and toward the right 

 side, and is continued posteriorly through the body cavity 

 as the dorsal aorta, giving off principal branches to all the 

 important visceral organs, and to the legs. 



The Skeleton. Study the sparrow's skeleton from dis- 

 articulated bones. Have a mounted skeleton at hand for 

 reference. Note the lightness of the bones. Hold some 

 of them up to the light, and observe the air spaces in 

 them. Note that the most striking peculiarities of the 

 skeleton are in the bones of the pectoral and of the pelvic 

 regions, modifications in the one region adapting the fore 

 limbs for flight, and in the latter adapting the hind limbs 

 for supporting the entire weight of the body in walking. 



The axial part of the skeleton, as in all vertebrates, is 

 the spinal column, with the skull at its anterior end. 



I. The Skull. Study the skull. Observe the large 

 orbits dividing it into a posterior cranial region and an 

 anterior facial region. Observe that the orbits are sepa- 

 rated from each other by an incomplete interorlital septum. 

 Observe that the cranial cavity opens widely into the 

 posterior dorsal part of both orbits. This large opening 

 was closed in life by a membrane, but the smaller ones 

 beneath it are foramina for the exit of cranial nerves. 

 At the back of the cranium find the foramen magnum, and 

 just beneath this the single occipital condyle, a minute 

 knob of bone for articulation with the first vertebra. 

 On either side of the condyle are very minute foramina 

 for the exit of other cranial nerves. 



Note how the lines of the skull converge toward the 



