NUMERICAL VARIATION IN THE HUMAN SPINE. 305 



side. Moreover the rib in this case is peculiar, and remarkable in that it resembles closely 

 one figured by Gruber. It is narrow, twisted beyond the tubercle so as to bring the inner 

 edge up with a prominent scalene tubercle and a deep groove before and behind it. The 

 features of the rib are sharply cut. It may be justly said that one is not justified in de- 

 scribing a type from two specimens ; nevertheless these two specimens are among the best 

 instances of cervical ribs. An unperfect 1st thoracic is very different. It is flat, not 

 twisted, and without either a prominent scalene tubercle or clear grooves. It is of a more 

 negative character. Wliile some moderately developed cervical ribs have something of 

 the twisted appearance of those first mentioned, others ai'e very like the featureless 

 imperfect 1st thoracics. It is absolutely impossible in many cases to distinguish, on an 

 isolated specimen, between a medium-sized cervical rib and a rudimentary thoracic one. 

 The resemblance between the cervical rib in 267 and the thoracic in 9379-38 has been 

 mentioned; the former is rather the more like a normal 1st rib. The rudimentary 1st of 

 A-4 and that from tlie left of the 7th vertebra of H-3, which i.s probably to be 

 similarly interpreted, resemble each other and that of 9379-38 very closely. 



H-3 is a very interesting and perplexing case. If the ribs of the 7th vertebra are to 

 be considered cervical, we probably have here another instance of a cervical rib of the 

 kind found in 202, though in the absence of the sternum it cannot be certain. I incline, 

 however, to consider them as thoracics placed too high, one of them being rudimentary. 

 Lane (85) reports an interesting case of the converse condition, in which the 8th verte- 

 bra bore on one side a ril) which he considers cervical, that from the 9th being practically 

 a normal 1st thoracic one. Leboucq ('96-98) also reports two cases, considered later in 

 another connection (p. 306) , in which the Stli vertebra bears rudimentary ribs quite like 

 cervical ones. These cases certainly point strongly to the likelihood that vertebrae of 

 different numbers at this end of the thorax also may assume similar features. They 

 show, moreover, how unsatisfactory the terms " cervical " and " thoracic " are in this 

 connection. 



Bicipital ribs sometimes occur and may be due to the fusion of a cervical rib with a 

 1st thoracic, or to the fusion of a 1st thoracic with the 2d. An instance of each is pre- 

 sented in 649 and in the incomplete specimen C-1, respectively. In the former the cer- 

 \ical rib soon joins the other, which presents no marked enlargement of its shaft, but the 

 latter specimen shows a great broadening. Indeed it is evident that there are two ribs 

 united even before it branches at the front into a normal 1st and 2d. Several instances 

 of this latter condition have been described, but for the most part without conclusive data 

 as to the number of the ribs. They have, however, a general family likeness and, more- 

 over, one point of resemljlance which perhaps has not been noted. It is the nearness of 

 the two heads to one another. In this specimen they both rest on the 8th vertebra. 

 This last point is very striking in all illustrations (Tui'uer, '83 ; Lane, '84) . While I 



