154 THE SKELETON. 



anterior arch is formed by the gradual extension forward and ultimate junction of 

 the two neural processes. 



The Axis (Fig. 120) is developed by six centres. The body and arch of this 

 bone are formed in the same manner as the corresponding parts in the other ver- 

 tebrge : one centre (or two, which speedily coalesce) for the lower part of the body, 

 and one for each lamina. The odontoid process consists originally of an extension 

 upward of the cartilaginous mass in which the lower part of the body is formed. 

 At about the sixth month of foetal life two osseous nuclei make their appearance 

 in the base of this process: they are placed laterally, and join before birth to 

 form a conical bilobed mass deeply cleft above ; the interval between the cleft and 

 the summit of the process is formed by a wedge-shaped piece of cartilage, the base 

 of the process being separated from the body by a cartilaginous interval, which 

 gradually becomes ossified at its circumference, but remains cartilaginous in its 

 centre until advanced age. 1 Finally, as Humphry has demonstrated, the apex of 

 the odontoid process has a separate nucleus, which appears in the second year and 

 joins about the twelfth year. In addition to these there is a secondary centre for 

 a thin epiphysial plate on the under surface of the body of the bone. 



The Seventh Cervical. The anterior or costal part of the transverse process 

 of the seventh cervical is developed from a separate osseous centre at about the 

 sixth month of foetal life, and joins the body and posterior division of the trans- 

 verse process between the fifth and sixth years. Sometimes this process continues 

 as a separate piece, and, becoming lengthened outward, constitutes what is known 

 as a cervical rib. 



The Lumbar Vertebrae (Fig. 121) have two additional centres (besides those 

 peculiar to the vertebrae generally) for the mammillary tubercles, which project 

 from the back part of the superior articular processes. The transverse process of 

 the first lumbar is sometimes developed as a separate piece, which may remain 

 permanently unconnected with the remaining portion of the bone, thus forming a 

 lumbar rib a peculiarity which is rarely met with. 



Progress of Ossification in the Spine generally. Ossification of the laminae of 

 the vertebrae commences at the upper part of the spine, and proceeds gradually 

 downward. Ossification of the bodies, on the other hand, commences a little 

 below the centre of the spinal column (about the ninth or tenth dorsal vertebra), 

 and extends both upward and downward. Although, however, the ossific nuclei 

 make their first appearance in the lower dorsal vertebras, the lumbar and first 

 sacral are those in which these nuclei are largest at birth. 



Attachment of Muscles. To the Atlas are attached nine pairs : the Longus 

 colli, Rectus capitis anticus minor, Rectus lateralis, Obliquus capitis superior and 

 inferior, Splenius colli, Levator anguli scapulae, First Intertransverse, and Rectus 

 capitis posticus minor. 



To the Axis are attached eleven pairs : the Longus colli, Levator anguli 

 scapulae, Splenius colli, Scalenus medius, Transversalis colli, Intertransversales, 

 Obliquus capitis inferior, Rectus capitis posticus major, Semispinalis colli, Mul- 

 tifidus spinae, Interspinales. 



To the remaining vertebrae, generally, are attached thirty-five pairs and a sin- 

 gle muscle: anteriorly, the Rectus capitis anticus major, Longus colli, Scalenus 

 anticus medius and posticus, Psoas magnus and parvus, Quadratus lumbo- 

 rum, Diaphragm, Obliquus abdominis internus, and Transversalis abdominis 

 posteriorly, the Trapezius, Latissimus dorsi, Levator anguli scapulae, Rhomboideus 

 major and minor, Serratus posticus superior and inferior, Splenius, Erector spinae, 

 Ilio-costalis, Longissimus dorsi, Spinalis dorsi, Cervicalis ascendens, Transversalis 

 colli, Trachelo-mastoid, Complexus, Biventer cervicis, Semispinalis dorsi and colli, 

 Multifidus spinae, Rotatores spinae, Interspinales, Supraspinales, Intertransversales, 

 Levatores costarum. 



1 See Cunningham, Journ. Anat., vol. xx. p. 238. 



