This section is from the book "Applied Anatomy: The Construction Of The Human Body", by Gwilym G. Davis. Also available from Amazon: Applied anatomy: The construction of the human body.
When suppuration occurs in the middle or proximal phalanx the pus may occupy the tissue between the skin and tendon and not involve its sheath, hence is not liable to extend rapidly. When the end phalanx is affected the affection is known as panaris, whitlow, felon, etc. The pulp of the finger resembles that of the heel, the scalp, the palm of the hand, etc., in the fact that the under surface of the skin sends off firm fibrous bands or fibrils which are attached to the parts beneath. The spaces between these fibrils are filled in with fatty tissue and vessels, nerves and lymphatics (Fig. 381). Infection begins in the skin through some small wound, as the tearing of the nail, pin-punctures, etc., and involves the fatty tissue beneath. If exit is not given to the pus it is often unable to break through the hard skin on the surface. Since the fibrous bands prevent swelling to any extent, it burrows deeper and involves the periosteum along which it proceeds to the region of the joint, here it may enter the sheath of the tendon when it rapidly proceeds upward as far as the sheath extends.
Fig. 380. - Palmar bursa and sheaths of the flexor tendons distended with wax.
Fig. 381. - Longitudinal section of the end of a finger, showing the pulp and mode of termination of the tendons in the distal phalanx.
Bone felons are not as a rule primary in their origin, unless syphilitic in character, but arise secondarily by extension from the skin above.