TUBEECULOSIS OF BONES. 21 



a pathway in the latter form of invasion. The sheath of the 

 optic nerve is connected with the lymphatics of the orbit and eye ; 

 the sheath of the auditory nerve is in communication with the 

 perilymph spaces of the internal ear. The olfactory nerve sheaths 

 are intimately connected with the lymphatics of the olfactory 

 mucous membrane. 



The spinal meninges usually suffer in company with the 

 meninges of the brain, but may be involved alone as the result of 

 the invasion by a tuberculous focus in the body of a vertebra, and 

 in the same way the spinal cord may become locally tuberculous. 



Of the organs of the senses the ear is open to direct infection 

 along the Eustachian tube or to invasion from the meatus or 

 invasion by means of the blood stream. 



The posterior part of the eye usually suffers in a blood-borne 

 tuberculosis, the richly vascular choroid affording a nidus. The 

 affection is then bilateral. Unilateral affection of the anterior 

 parts of the eye points rather to local infection from without. The 

 conjunctiva and lachrymal apparatus may be similarly infected. 

 The preauricular, submandibular, and cervical lymphatic glands 

 are enlarged in these cases of anterior local infection. The vascular 

 iris is liable to suffer in common with the back of the eye in 

 general infection, also may be invaded from the front in local 

 infection. The rarity of local tuberculous infection is due to 

 the efficiency of the lachrymal apparatus and the protection 

 afforded by the squamous epithelium of the conjunctivas. 



Tuberculosis of the bones and joints is generally secondary to 

 a focus elsewhere. Infection is conveyed to the bone or joint 

 involved by the lymphatic or vascular systems, usually by the 

 latter. As a rule the primary focus is in the bronchial glands 

 or in the lung. The petrous bone and mastoid may be 

 directly infected by way of the Eustachian tube or the external 

 auditory meatus. The carpal and tarsal joints may, in some 

 instances, be invaded directly from contiguous tendon sheaths. 

 Cancellous bone, from its richer blood supply, is more likely to 

 suffer than bone which is compact; vascular, rapidly growing 

 epiphyses are especially liable to infection, particularly where 



