OF BAL^NOPTERA MUSCULUS. 



215 



Fijr. 3. — 3d Cervical Vertebra. 



has a slight central depression on its posterior extremity. This depression becomes more 

 marked in the succeeding ones, and after the 16th a siuiilar one is seen on the anterior 

 extremity. The 23d is convex posteriorly, and the three remaining are too evidently irregu- 

 lar to deserve description. The 3d cervical presents a depression in the upper and lower 

 border, which is marked by a 

 prominence in the median line, 

 that below being double, but 

 single in those following. In 

 the 4th the depressions are 

 very slight, and in the 5th are 

 wanting. The superior median 

 prominence continues through- 

 out the cervicals, though grad- 

 ually decreasing ; the inferior 

 becomes more marked, and in 

 and after the 4th dorsal is very 



striking, showing a prominent longitudinal ridge. In the 5th, 6th, and 7th it gradually 

 disappears, but returns in the loth, and increases till it attains its greatest development at 

 about the middle of the lumbar region. In the 15th lumbar it shows signs of bifurcation 

 towards the posterior end. In the 1st caudal these prominences become marked for the 

 attachment of the chevron bones, and we now have two lines with a median depression 

 between them. In the 4th caudal lesser prominences appear at the anterior end. The 

 depression continues to grow deeper, and as the bodies become shorter the elevations on 

 the ends of these lines are naturally brought nearer together, till in the 13th they unite, 

 forming a ridge perforated by a foramen corresponding to the previously existing notch 

 In the 15th the bone has become so much modified that there is merely a single protu- 

 berance on either side of the 

 foramina which enter the in- 

 ferior surflice of the bone, and 

 presently this disappears en- 

 tirely. The superior surface of 

 the body forming the floor of 

 the spinal canal loses, as al- 

 ready stated, the central ridge 

 with the first dorsal vertebra?? 

 and after that is marked by a 

 concavity in its centre, its ante- 

 erior and posterior borders re- 

 maining straight. This concavity is most marked about the middle of the dorsal region. 

 The proportions of the bodies can be seen by reference to the table. At first they are 

 broad and thin in the cervical, but later the height and length increase, till in the anterior 

 caudal region the three diameters are not very different. In the 14th caudal the height for 

 the first time surpasses the breadth. In the 15th dorsal the length approaches to within 1-4 

 of an inch of the height, but as the latter then increases the discrepancy continues till we 

 reach the 23d caudal. These proportions agree very well with those to be deduced from 



Fig. 4. — 4th Cervical Vertebra. 



