THE NECK 



a part of the body and as a fused complex virtually constitutes a thoracic 

 vertebra without ribs. The series has probably become as short as it can 

 while at the same time accommodating essential muscles which are at- 

 tached at this point, as well as allowing for the emergence through fora- 

 mina of the cervical nerves. The stimulus has been for the thorax to en- 

 gulf the neck and to this extent the latter has experienced squeezing, but 

 from a morphological or evolutional rather than a mechanical sense. Al- 

 though there is no reason for considering the balaenid as any older than 

 the balaenopterid stock the cervicals in the former group have fused more 

 completely probably because the larger mass of the head has increased 

 the strength of the stimulus for fusion. Normally in the former they 

 are completely fused but Flower (1876) has stated that occasionally the 

 seventh is free. The cervicals of the cachalot (Physeter) are also usu- 

 ally fused, I believe, but this is not established for the reason that in 

 some of the few specimens known the atlas is free ; and this is a unique 

 situation among Cetacea, for in all other whales fusion of the cervical 

 elements first takes place anteriorly and then progresses toward the rear. 

 In those specimens of the manati which show fusion of two or three 

 cervicals the atlas is said always to remain free, however. 



In the above discussion account has not been taken of the pygmy 

 right whale (Neobalaena) or pigmy sperm whale (Kogia) for the rea- 

 son that these are depauperate, freakish forms. The former is anomalous 

 in that the first thoracic vertebra lacks ribs. In other words, it has eight 

 cervicals, which indicates an exactly opposite trend from that exhibited 

 by all other whales. This circumstance is very puzzling, but it is felt that 

 one exception does not overthrow the arguments that have been ad- 

 vanced. 



Before closing this chapter brief mention should be made of other cer- 

 vical muscles not yet discussed. During swimming the majority of the 

 subcervical muscles of whales act in antagonism to the supracervical ones, 

 but many of them have other functions not connected with locomotion. 

 Thus the hyoid complex is very powerful in odontocetes and these doubt- 

 less assist in depressing the head, but whether this is now their primary 

 stimulus cannot be told. They must also be used in the deglutition of 

 bulky food, but this is hardly to be reckoned with in Mysticeti, especially 

 the balaenopterids, because their esophagus is relatively so small, but in 

 this group the depression of the head can probably be largely brought 

 about by flexion of the superficial gular musculature (previously dis- 

 cussed) operating upon the mandibular tip. The hyoideal as well as 

 other small muscles of the prevertebral and lateral parts of the neck are 



[151] 



