CHAP. IV.] 



SPINAL NERVES : BIRDS. 



133 



commonly bore a resemblance to the original pattern of the plexus, 

 a phenomenon which Furbuinger has called "imitatory Homo- 

 dynamy" or u Parhomology " of the plexus 1 (I. c. p. 245). 



Correlation between the constitution of the brachial plexus and 

 the position and number of moveable cervical ribs. 



Anser cinereus, var. domestica. Upon this point Furbrin- 

 ger has made a series of important observations, especially in the 

 Goose, which enabled him to state that there is, within limits, a 

 certain correlation between the composition of the brachial plexus 

 and the development of the ribs of this region. Speaking gener- 

 ally, those individuals in which the plexus was formed in a more 

 anterior position usually shewed a fairly developed cervical rib on 

 the 18th vertebra (Anser) t and even as in Fig. 12, I, a very short 

 but moveable rib on the 17th vertebra ; and in such cases the 19th 

 vertebra generally bore the first true sternal rib. On the other 

 hand, examples with a more posterior development of the brachial 

 plexus shewed not only an entire absence of moveable ribs on the 

 17th, but even a considerable reduction in the size of the ribs of 

 the 18th and 19th vertebrae, so that these became "transitional' 

 in character, leaving the 20th vertebra as the first vertebra bearing 



xv xv7 xMic^^CrXisst 1 xx x\i xvn xwcrXixcr xx 



Fig. 12. Diagrams of brachial plexus and cervical ribs in two Geese {Anser 

 cinereus, var. domestica) after Furbringer (being his specimens D, left, and G, right). 



I. Case in which the 17th and 18th vertebrae bear cervical ribs and the 19th 

 bears the first sternal rib. II. Case in which the 17th and 18th vertebra bear 

 cervical ribs, and the 20th bears the first sternal rib. 



ax axillaris, bri brachialis longus inferior, brs brachialis longus superior, 

 cbri coraco-brachialis internus, ci cutaneus brachii inferior, c-x cutaneus brachii 

 superior, ic intercostals, Id latissimus dorsi, p pectoralis, rh rhomboideus, sbse sub- 

 scapulars, srpr nerves to levator scapula? and serratus profundus, srsp nerves to 

 serratus superficialis, stc sterno-coracoideus. 



1 The principle denoted by these expressions is nearly the same as that here 

 expressed in the term Homceosis, which is perhaps more convenient as being a more 

 inclusive expression. 



